Field of the Invention
The present invention relates to a fuel injection device for use in, for example, a gas turbine engine and, more particularly, to the fuel injection device equipped with a complex fuel injection device comprised of a plurality of fuel nozzles.
Description of Related Art
In recent years, in consideration of the environment, there is a need for a reduction of emissions such as NOx (nitrogen oxide) emitted from gas turbine engines. A fuel injection device of the conventional aircraft gas turbine combustor is of a diffusive combustion type, and since in the diffusion combustion, the burning reaction takes place based on the stoichiometric mixture ratio, the flame temperature tends to increase. Considering that the emission of NOx is known to exponentially increase with the increase of the flame temperature, lowering of the flame temperature appears to effectively suppress the emission of NOx. However, in the current situation of the propensity for high temperature and high pressure in the gas turbine, further suppression of the emission of NOx with the conventional diffusive combustion method is limited.
In order to lower the flame temperature, a fuel injection device of a lean premixed combustion method is considered effective. The lean premixed combustion method is known to be a method of burning an air-fuel mixture in which the ratio of fuel relative to air is lowered, and the lean combustion according to this method contributes to a considerable reduction of the flame temperature as compared with that afforded by the conventional diffusive combustion method. On the other hand, however, the lean premixed combustion method tends to result in an instable and incomplete combustion of the air-fuel mixture because of the relatively low flame temperature. In view of this, a concentric fuel injection device has been used to realize a low NOx emission, in which while a pilot fuel injector is located on an inner side and a main injector is located coaxially with, and outer side of the pilot fuel injector. In the concentric fuel injection device, the diffusive combustion method with the pilot fuel injector is used to maintain a stable combustion at a low power operation, while the lean premixed combustion method with the main fuel injector is used in addition to the diffusive combustion with the pilot fuel injector at a high power operation.
In the concentric fuel injection device, even at low power settings at which only the pilot injector operates, a large amount of air flows through a flow path in the main injector. Accordingly, there is a possibility that the air and pilot combustion interfere with each other and the combustion efficiency, the ignition, and the flame stability of the pilot injector is lowered. In order to overcome the problem, for example, there have been the following proposals: a pilot combustion region and a main combustion region are greatly separated from each other and it is configured that the pilot combustion region and the main combustion region appropriately interfere with each other at intermediate power settings while suppressing interference between air in a main path and pilot combustion at low power settings, thereby achieving stable combustion in the main combustion region (see, e.g., Patent Document 1); and a fuel is intensively injected to a reverse-flow region on an axis of a combustion chamber, thereby improving the combustion efficiency at low power settings (e.g., JP Patent Application No. 2011-125481).